Many lithography systems use transmissive masks to image a pattern on a wafer. Light which passes through transparent portions of the mask may form a pattern on a photoresist material on the mask. Lithography systems may also use reflective masks to image a pattern on a wafer. Light may be reflected off of a reflective mask rather than passing through the mask, as with a transmissive mask.
Light may be directed to a reflective mask at an incident angle off normal. Due to this angle of incidence, features parallel to the plane of incidence (e.g., horizontal features) may exhibit a shadowing effect. Features parallel to the plane of incidence (e.g., vertical features) may not exhibit the shadowing effect.
The difference in shadowing effect between the horizontal and vertical features may make the horizontal features projected onto the imaging plane larger than the vertical features. To compensate for this effect, the horizontal features may be drawn on the mask such that they are scaled smaller than the vertical features.